Silverlight.net
Obviously, the official Microsoft Silverlight webpage is the first place you should go to showcase your projects. Every Silverlight developer should visit this page before doing anything else. You can find lots of cool Silverlight Applications on this website. It also contains a tutorial section, a showcase section, forum, and much more.
Silver Arcade
SilverArcade is a relatively new website dedicated to Silverlight Games. You have to submit games through email because there is no automatic game submission form yet. Even so there are already lots of cool games up on the website. The page design and interface is superb. They even pay you for your submissions through paypal. I’m sure this page is going to be very popular very soon.
Mashooo
My favorite Silverlight Games website. Uses ad-revenue sharing model. I like it because the admin always gives very kind and helpful comments. If you put your game up there now you might even qualify for their S-Prize contest which features prizes over $10,000! Whoa!
Silverlight Club
This looks like a more commercialized Silverlight website. Uses ad-revenue sharing model as well – they give you 90% of you share! You can upload not only games, but any types of applications as long as they are cool and they are on Silverlight platform. Also has a contest going on with prizes worth thousands of dollars.
GameJolt
Very nice interface, very well established. This website hosts all kinds of games including Silverlight, Flash, Java Applet, Free downloadable games etc. Lots of good articles about game development. Definitely give it a try.